The best way to go about your business in a store is to know the person selling/trading the cards from/through the store...
A lot of owners are previous/current players of the games they sell... note this is not always the case...
What you can do is talk to the store owner a bit, let him/her know what you're wanting to do, and make sure you mention the word "buy"...
They do want to know that you're a customer, and not someone who will generate nil cash from your own pocket - though if you have high-dollar stuff for trade, it helps because they know they can sell it to others...
as for the other players in the stores - ask the owner/manager if they have tournaments, if not, is there a place they know of... don't mention anything about the other stores you know about - let them tell you what they know...
Personal note - I am the only one allowed to sell cards in the shop I play in - and this isn't discriminatory - I spend plenty of money at the shop, but the owner understands I have stuff he doesn't and allows me to sell - though I do my best to keep this low profile... The main reason I'm allowed to do so is because I asked his permission before doing so, and told him I would only trade on items that he also had in the store...
If you try to sell at the store - do it outside the business, unless you know it is otherwise permitted... I've even known shops that asked for a commission on deals made within the store - but this was on the honor method anyway...
If you're looking for the people experience on trading and playing and buying be patient and maybe call the stores and ask them...
If you just want to begin trading/buying - let the CPA know what you're looking for by posting a have/want list in the trading forum...
and as for gizmo - go to the members list(top menu bar on your screens) and then select "G" i think Gizmo is on the second page for "G"s...
Hope all this helps...
train.